Fuel injectors for gas turbine engines on an aircraft direct fuel from a manifold to a combustion chamber of a combustor. The fuel injector typically has an inlet fitting connected to the manifold for receiving the fuel, a fuel nozzle located within the combustor for spraying fuel into the combustion chamber, and a housing stem extending between and interconnecting the inlet fitting and the fuel nozzle. The housing stem typically has a mounting flange for attachment to the casing of the combustor.
Fuel injectors are usually heat-shielded because of a high operating temperatures arising from high temperature gas turbine compressor discharge air flowing around the housing stem and nozzle. The heat shielding prevents the fuel passing through the injector from breaking down into its constituent components (i.e., “coking”), which may occur when the wetted wall temperatures of a fuel passage exceed 400° F. The coke in the fuel passages of the fuel injector can build up to restrict fuel flow to the nozzle.
Heretofore, injector nozzles have included annular stagnant air gaps as insulation between external walls, such as those in thermal contact with high temperature ambient conditions, and internal walls in thermal contact with the fuel. In order to accommodate differential expansion of the internal and external walls while minimizing thermally induced stresses, the walls heretofore have been anchored at one end and free at the other end for relative movement.
U.S. Pat. No. 6,321,541 discloses an injector configuration including an elongated laminated feed strip that extends through the stem to the nozzle. The laminate feed strip and nozzle are formed from a plurality of plates. Each plate includes an elongated feed strip portion and a nozzle portion. Selectively etching the plates allows multiple fuel circuits, single or multiple nozzle assemblies and cooling circuits to be easily provided in the injector. Like in the previously mentioned injectors, the feed strip has convolutions along its length to accommodate differential thermal expansion arising from the extreme temperatures to which the injector is exposed.